1. Field of the Invention
The present invention relates to an optical disk, and more particularly, to a recording medium having wobbled groove tracks which are out of phase with wobbled land tracks, a servo controlling apparatus for stably controlling movement of a pickup using a wobble signal picked up from the recording medium, and a method thereof.
2. Description of the Related Art
In order to record and/or reproduce images of a high definition television (HDTV) level, large-capacity recording and high-speed reproduction are necessary. Thus, there has been increasing demand for multi-media technology by which a large amount of information can be recorded and/or reproduced on a recording medium such as a rewritable or read-only high-density digital versatile disk (HD-DVD).
In order to satisfy the demand for large-capacity recording and high-speed reproduction, various kinds of methods have been proposed. For example, the area of a disk or the revolution speed may be increased, which is, however, impractical due to an increase in the size or volume of a disk or disk player and an increase in the manufacturing cost. Thus, increasing the recording density per unit area is more effective and desirable.
The size of a laser spot is proportional to the laser wavelength (λ) and is inversely proportional to the numerical aperture (NA) of an objective lens. Thus, in order to increase the recording density per unit area, the laser wavelength must be reduced or a track pitch must be reduced using an objective lens having a high NA. In rewritable or read-only HD-DVDs which are likely to see widespread use in the near future, the track pitch is reduced to about 0.30 to 0.34 μm. Thus, it is important for an optical pick-up unit (hereinafter, to be referred to simply as a pickup) to move to a desired position where data is written or read, and for it to be positioned thereon without error.
In disks to which a land/groove recording method is applied, the capability of a pickup to locate a basic recording unit or a specific area is largely affected by the configuration and disposition of addressing pits or grooves. Thus, in conventional optical disks adopting a land/groove recording method, in order to locate a physical area without error, both a physical address area and a wobble signal having a predetermined frequency are used in addressing. In the case where a physical identifier (ID) header is recorded on a disk, it must be shifted by half a track pitch from the center of a land or groove track to be recorded. Thus, the location of the physical ID header is used in accessing a desired land or groove track.
A conventional recording medium having wobbled groove tracks and a wobble signal picked up from the recording medium will be described, in conjunction with FIGS. 1 through 2B.
FIG. 1 illustrates a conventional recording medium having wobbled groove tracks, wobbled land tracks and physical identifier (PID) areas, in which the wobbled groove tracks and wobbled land tracks each have the same frequency and phase. Since a PID is recorded after it is shifted from the center of a land or groove track by half a track pitch, it is used for accessing a desired land or groove track. In other words, it is possible to know whether a track currently being picked up is either a land track or a groove track by using locations of the first PID through the fourth PID prepitted on physical address areas, which are denoted by Header 1 field, Header 2 field, Header 3 field and Header 4 field in the drawing, respectively. Also, the locations of the first PID through the fourth PID can be used as land/groove switching information. In FIG. 1, reference character N denotes the number of sectors for each track. Also, the recording medium shown in FIG. 1 includes a mirror field next to PIDs.
If a track is wobbled, as shown in FIG. 1, a wobble signal can be obtained as a difference signal of two signals output from a photo detector, which typically comprises a bi-divisional photo diode, due to diffracted light from a land track and a groove track. Deviation of a light axis or the tilt of a disk can be obtained using the wobble signal. In other words, as shown in FIG. 2A, a wobble signal is not generated at either a groove track or a land track in a first channel (CH1) corresponding to the sum of two signals output from the photo detector. As shown in FIG. 2B, a wobble signal is generated in a second channel (CH2) corresponding to the difference between two signals of the photo detector. Thus, the wobble signal is generated at the groove track and the land track only in the second channel CH2 corresponding to the difference between signals at opposite sides in view of a line parallel to the track. Here, the wobble signal detected from the land track (hereinafter, to be referred to simply as a land wobble signal) and the wobble signal detected from the groove track (hereinafter, to be referred to simply as a groove wobble signal) have the same frequency and phase.
Since the physical ID header (hereinafter, to be referred to simply as a PID) is shifted by half a track pitch from the center of a land or groove track to be recorded, in the case of one-beam mastering, position control depending on beam shift and light intensity are different between formation of a groove track and formation of a PID. Even in the case of two-beam mastering, it is quite difficult to precisely control beam position and light intensity. Also, if tilting of a disk occurs, since reproduction characteristics of PIDs in a land track and a groove track are different from each other, additional tilt correction methods must be adopted.